This invention relates to the use of an ultrasonic transmitter and receiver and a microprocessor to accurately detect the presence of an object. There are many ultrasonic devices that are able to determine the presence or distance of an object. One such device transmits an ultrasonic burst and at the same time sets a latch signal. When the first echo is received by the receiver the latch signal is reset. The duration of the latch signal is proportional to the distance between the device and the target that caused the echo. Any echo received after the first echo and before the transmission of another tone burst has no effect.
The problem with this approach is that transient background noise may be picked up by the receiver and registered as an echo, causing this device to be unreliable. In addition, when used as a detector, the background environment may have characteristics that are continuously changing which affect the echo, causing the device to be unreliable. Another problem with this approach is that if the target object absorbs the transmitted frequency the device will fail to detect the target.
Another device used for this purpose emits bursts of ultrasound that are composed of different frequencies. The frequencies are chosen so that if the target absorbs one of the transmitted frequencies it will not absorb all of the other frequencies. Like the above device, the secondary echoes being received after the first echo following a transmitted burst has been received, have no effect. A problem with this device is that the receiver must have a broader bandwidth in order to receive all of the transmitted frequencies. The reception of a broader spectrum of frequencies results in the receiver picking up more background noise, making the device more easily affected by background noise.
Another problem with the above mentioned devices is that in an environment with complex shapes, these detectors will only detect the part of the environment that produces the first echo since they use only the first echo received following a transmitted burst, ignoring any secondary echoes. If an object is placed in a position in the environment so that it would not generate the first echo it would not be detected.
Many detectors have a narrow detection angle which simplifies the background environment.